Timing alignment in an LTE system

ABSTRACT

A method for use in a user terminal in a cellular communications system. According to the method, the user terminal applies a first timing advance value to its transmissions to a controlling node, and the user terminal requests communication with the controlling node in a contention based procedure by transmitting an access request (MSG  1 ), in response to which the controlling node transmits an initiation message (MSG  2 ) along with a second timing advance value. According to the method, the user terminal uses the first timing advance value if the user terminal loses the contention based procedure, i.e. if the controlling node subsequently continues the initiated communication with said other user terminal.

This application is a continuation of U.S. application Ser. No.14/941,711, filed 16 Nov. 2015, which is a continuation of U.S. patentapplication Ser. No. 12/741,328, filed 4 May 2010, now issued as U.S.Pat. No. 9,204,468, which is a national stage application ofPCT/SE2008/050685, filed 9 Jun. 2008, which claims the benefit of U.S.Provisional Application Ser. No. 60/985,379, filed 5 Nov. 2007, thedisclosures of each of which are incorporated herein by reference intheir entirety.

TECHNICAL FIELD

The present invention discloses a method for use in a user terminal in acellular communications system, where the user terminal applies a firsttiming advance value to its transmissions to a controlling node.

BACKGROUND

In the forthcoming cellular system known as LTE, Long Term Evolution,the downlink transmissions, i.e. transmission to the users in a cell,will use so called OFDM modulation, Orthogonal Frequency DivisionMultiplex, while the uplink transmissions, i.e. transmission from theusers in a cell, will use either OFDM or OFDM-like technologies, such asDFTS-OFDM, a transmission technology which allows for orthogonalmultiple access in time as well as in frequency.

Transmissions to and from users in a cell are made to/from a controllingnode of the cell, this node in LTE being known as eNodeB, “evolvedNodeB”. Users in an LTE system are sometimes referred to as UEs, “UserEquipment”.

In order to preserve the orthogonality needed in an LTE system,transmissions from the UEs in a cell need to be time aligned when theyarrive at the eNodeB, i.e. the transmissions from the UEs in the cell ofthe eNodeB need to arrive more or less simultaneously at the eNodeB.

Since the different UEs in a cell may be located at different distancesfrom the eNodeB of the cell, the UEs need to initiate theirtransmissions at different points in time in order for theirtransmissions to arrive simultaneously at the eNodeB. For example, a UEwhich is at the cell edge needs to start its transmissions prior to a UEwhich is closer to the eNodeB.

The issue of when to start the transmissions in the different UEs in acell can be handled by means of a so called “timing advance”, in otherwords an “offset” value in time at which a UE needs to start itstransmissions relative to a nominal transmission time specified by theeNodeB.

The value of the timing advance for a UE can be determined by the eNodeBby means of measuring the arrival of uplink transmissions from the UE,and the eNodeB then transmits the timing advance value to the UE withregular updates, since the UE may move around in the cell.

If a UE does not make any transmissions for a period of time, the timingadvance needed by the UE becomes uncertain, for example due to possiblemovement away from the eNodeB of the UE. In order to avoid unaligned UEtransmissions, there is therefore typically in an LTE system a timer inboth the eNodeB and the UE, which determines when a UE falls “out ofsynchronization” in uplink. Thus, if a UE has not received a new timingadvance command from its eNodeB during a specified period of time, theUE will consider itself out of synchronization.

A UE which is out of synch and needs to initiate communication with itseNodeB will avail itself of a procedure known as Random Access, aprocedure which is used in a number of cases, such as, for example:

-   -   Resynchronization,    -   Incoming handover,    -   Scheduling request (for a UE that is not allocated any other        resource for contacting the base station).    -   Initial access, for UEs in the LTE_IDLE or LTE_DETACHED states.

One of the Random Access procedures defined for LTE systems is a socalled contention based procedure, and can briefly be described asfollows:

The UE starts the Random Access procedure by randomly selecting one ofthe preambles available for contention-based random access, and thentransmits the selected random access preamble on the physical randomaccess channel, PRACH, to the eNodeB.

The eNodeB acknowledges reception of the preamble by transmitting aresponse, which includes a timing advance value update to be used infuture transmissions from the UE.

A problem can arise during the Random Access procedure if more than oneUE happens to select one and the same preamble and transmit at the sametime, or rather, if the transmissions arrive simultaneously at theeNodeB. In such a case, the eNodeB will resolve the conflict bytransmitting a so called contention resolution message, which informsthe UEs of which one of them has “won” the contention based procedure,and may thus communicate with the eNodeB.

However, although the contention conflict has been resolved, a problemwill remain: the timing advance value update which was transmitted bythe eNodeB in response to the preamble is based on the transmission fromthe “winning” UE, but has been adopted by all of the UEs involved in the“contention conflict”. Thus, one or more UEs may have erroneous timingadvance values. This is particularly bothersome in the case of a UEwhich has entered the contention based procedure due to a SchedulingRequest, since the UE in that case will have been “in synch” prior tohaving entered the procedure, but may come out of the procedure “out ofsynch”.

SUMMARY

As has emerged from the explanation above, there is a need for asolution to the problem of timing advance values which will obviate atleast some of the problems mentioned above.

Such a solution is offered by the present solution in that it disclosesa method for use in a user terminal in a cellular communications system.

In the method of the invention, the user terminal applies a first timingadvance value to its transmissions to a controlling node, and the userterminal requests communication with the controlling node in acontention based procedure by transmitting an access request, inresponse to which the controllingnode transmits an initiation message ofthe requested communication along with a second timing advance value.

According to the method of the invention, the user terminal uses thefirst timing advance value if the user terminal loses the contentionbased procedure, i.e. if the controlling node subsequently continues theinitiated communication with another user terminal.

Thus, according to the method of the invention, the problem of users who“lose” a contention based procedure such as, for example, a randomaccess procedure, but who during the procedure have received a timingadvance intended for the “winner” of the procedure, is solved in thatthe “original” timing advance value is used if the user terminal losesthe procedure.

In one embodiment of the present invention, the user terminal uses thesecond timing advance value in a message which is subsequent to saidinitiation message, and in one version of this embodiment, the userterminal uses the second timing advance message if the user terminalwins the contention based procedure.

In another embodiment, the user terminal uses the first timing advancemessage if the user terminal wins the contention based procedure.

Also, in one version of the invention, the inventive method is appliedif the first timing advance value is considered valid by the userterminal, which for example, can be done by means of letting the timingadvance value in a user terminal be associated with a timer and beconsidered valid for the duration of said timer. The timer is suitablystarted upon reception of a predefined message from the controllingnode, so that each of the first and second timing advance values areassociated with respective first and second timers which have beenstarted upon reception of respective messages.

In a further version of the “timer embodiments”, the user terminal letsthe timer which is associated with the first timing advance valuecontinue running after receipt of the message associated with the secondtimer, and uses the timer value which is associated with the timingadvance value which is subsequently used. Thus, which timer that is usedis tied to the outcome of the contention based procedure, i.e. if theuser “wins” or “loses” the contention based procedure.

In another version of the “timer embodiment”, the user terminal savesthe value of the timer which is associated with the first timing advancevalue when it receives the second timing advance value, and if thecontrolling node subsequently continues the initiated communication withanother user terminal, the user terminal uses a timer value which is thesum of the saved value and the current value of the timer of the secondadvance value. In other words, the user terminal restarts the timer uponreception of the new timing advance value, but since it knows the valueof the “old” timer at the reset point, the user terminal can revert backto the “old” timer by adding the saved value of the “old” timer to thecurrent value of the “new” timer, if the user terminal “loses” thecontention based procedure.

These and other advantages and further embodiments will be described inmore detail below.

The invention also discloses a user terminal which works according tothe inventive method.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in more detail in the following, withreference to the appended drawings, in which

FIG. 1 shows a schematic view of a system in which the invention may beapplied,

FIGS. 2 and 3 show prior art in order to illustrate a problem,

FIGS. 4, 5 a and 5 b show flow charts which illustrate the invention,and

FIG. 6 shows a block diagram of a transceiver of the invention.

DETAILED DESCRIPTION

The invention will in the following be described with the use ofterminology from the LTE system, Long Term Evolution. It should howeverbe emphasized that this is done in order to facilitate the reader'sunderstanding, and should not be construed as limiting the scope ofprotection sought for the present invention, which can be applied toother cellular systems in which the same problems arise. Also, thebackground will be discussed briefly again in this section of the text.

FIG. 1 shows an overview of a system 100 in which the invention can beapplied. As shown, the system 100 comprises a number of cells, one ofwhich is shown as 110 in FIG. 1. Each cell can hold a number of users,two of which are shown in FIG. 1 as 120 and 130. The generic term forusers in an LTE system is “UE”, User Equipment, a term which will alsobe used here, and which is used in FIG. 1.

For each cell there is a controlling node, an eNodeB 140, which controlsthe traffic to and from the users in the cell. Traffic from the UEs tothe eNodeB is known as uplink traffic, UL traffic, and traffic in theother direction is known as downlink traffic, DL traffic.

As explained previously, in an LTE system, it is important fortransmissions from the different UEs in a cell to arrive simultaneouslyat the eNodeB of the cell. The UEs receive instructions from the eNodeBregarding when to make their UL transmissions, but as can be realized,and as can also be seen in FIG. 1, the arrival of an UL transmission atthe eNodeB will depend on the distance between the eNodeB and the UE inquestion. For example, simultaneous transmissions from the UEs 120 and130 will arrive at the eNodeB 140 at different points in time, with theUL transmissions from the UE 120 arriving before those of the UE 130.

For this reason, the LTE system employs a system of “timing advance” ofUL transmissions, so that a UE is informed by the eNodeB of a timingadvance value, i.e. an “offset” which should be applied to timinginstructions for UL transmissions. The timing advance value for a UE isdetermined by the eNodeB of the cell by measurements on UL transmissionsreceived from the UE at the eNodeB, and is signalled as a time alignmentcommand.

The notion of timing advance, and of different values for thisparameter, is illustrated in FIG. 2, by means of three time lines: thetop time line shows a nominal window for UL transmissions from the UEsin the cell 110 to the eNodeB 140. The nominal window extends between t₁and t₂. The middle time line shows a timing advance for the UE 120:since the UE 120 is at a certain distance from the eNodeB, the UE 120needs to make its transmissions between t′₁ and t′₂ in order for thosetransmissions to arrive at the eNodeB between t₁ and t₂. This can alsobe viewed as displacing the UL transmission window of UE 120 by anoffset in time, i.e. a timing advance, with a value of Δ₁ in FIG. 2.

The bottom time line in FIG. 2 shows the timing advance for the UE 130:since the UE 130 is quite far from the eNodeB, the UE 130 needs to makeits transmissions between t″₁ and t″₂ in order for those transmissionsto arrive at the eNodeB between t₁ and t₂. This can also be viewed asdisplacing the UL transmission window of UE 130 by a timing advance witha value of Δ₂, as shown in FIG. 2.

The invention is mainly intended for the contention based Random Accessprocedure, which is illustrated in FIG. 3, with the messages, “MSG”,being numbered as follows:

MSG 1: A random access preamble transmitted by a UE to the eNodeB.

MSG 2: A random access response from the eNodeB, including a timingadvance update, based on a measurement of message 1.

MSG 3: A scheduled transmission from the UE, based on the instructionsin message 2.

MSG 4: A contention resolution message from the eNodeB, which istransmitted in order to identify the UE which has “won” the contentionbased procedure.

If there has been a preamble conflict, which is resolved by message 4 asabove, the problem which the invention is intended to address can berealized: the timing advance value transmitted by the eNodeB in message2 is based on message 1 from the “winning” UE, but is applied to all UEsin the conflict. Thus, all UEs in the conflict but one, the winning one,will apply a timing advance value which is erroneous for them.

A basic idea of the invention is that in order to overcome this problem,a UE which requests communication with its eNodeB will use the timingadvance value that the UE had prior to requesting communication with theeNodeB if the UE loses the contention based procedure. Thus, if theeNodeB transmits an initiation message with a timing advance value, butthen continues the communication with another UE, for example if theUE's request for communication was part of a contention based procedurewhich the UE loses, the UE will use its “original” timing advance value.

A flow chart of this basic principle is shown in FIG. 4:

-   -   In step 402, the UE requests communication with the eNodeB by        means of transmitting MSG 1 of FIG. 3,    -   In step 405, the UE receives message 2, MSG 2, of FIG. 3, with        an accompanying timing advance value, T_(TA2),    -   In step 410, the UE loses the contention based procedure, i.e.        the controlling node continues the initiated communication with        another user terminal,    -   In step 415, the UE uses T_(TA1), in order to transmit messages        to the eNodeB.

In one version of the invention, the UE uses the original timing advancevalue, i.e. T_(TA1) if the UE loses the contention based procedure, butuses the “updated” timing advance value, i.e. T_(TA2), in the subsequentmessage shown as MSG 3 of FIG. 3. In a further version of thisembodiment, the UE will also use T_(TA2) if the UE “wins” the contentionbased procedure.

In another embodiment of the invention, the UE will use the originaltiming advance value, i.e. T_(TA1), if the UE “wins” the contentionbased procedure.

Preferably, the principle shown in FIG. 4 and the versions describedabove are only applied if the UE has a valid timing advance value whenit requests communication with the eNodeB. The notion of a valid timingadvance value can preferably be implemented as follows: the timingadvance values, e.g. T_(TA1) and T_(TA2), have a validity which is tiedto a timer, here referred to as a “timing alignment timer”, so that atiming advance value may become invalid due to the fact that the timingalignment timer has expired, i.e. when the timing alignment timer is notrunning. The timer is started when a specific predetermined message suchas, for example, the timing advance value is received from the eNodeB,and, in this case, a reason for the invalidity mentioned above is thatthe timer has expired. The timer or timers may also be started bypredetermined messages during an ongoing “data session” between theNodeB and the UE.

If a timer is used to determine the validity of the timing advancevalue, there will be a need for one timer for each of the timing advancevalues shown above, i.e. T_(TA1) and T_(TA2), and these timers will needto be handled in the following manner:

-   -   If the UE reverts back to the “old” timing alignment value        T_(TA1), a timing alignment timer should be used which reflects        the point in time that T_(TA1) was received from the eNodeB.    -   If the UE successfully completes the random access procedure and        uses the new timing alignment value T_(TA2), a timing alignment        timer should be used which reflects the point in time when        T_(TA2) was received from the eNodeB.

The invention proposes a number of different possibilities in order tocorrectly manage the timer of the timing advance value in the UE:

-   -   One solution is that the UE has two different timers running in        parallel during the completion of the contention based        procedure, and then selects the appropriate timer, depending on        whether or not the procedure is successful, i.e. if the UE        “wins” the procedure or not,    -   A second solution is to use a single timing alignment timer, but        to take a “snapshot” of the timer when the UE receives T_(TA2),        and to then restart the timer. It the procedure is unsuccessful        and the UE reverts back to T_(TA1), the UE adds the stored        snapshot of the timer to the current value of the timer,    -   A third solution is to use a single timing alignment timer, but        to take a “snapshot” of the timer when the UE receives T_(TA2),        and then apply a fixed value that reflects the time from        reception of T_(TA2) until the procedure either concludes        successfully or concludes unsuccessfully due to timeout. This        value could either reflect the minimum or maximum latency of the        remainder of the RA procedure.    -   In a fourth version, a UE which already has a valid timing        alignment value ignores the timing alignment value received in        the random access response message, and transmits subsequent UL        messages such as message 3 of FIG. 3 according to that timing        value.

FIG. 5 shows a flow chart of a generalized method of the invention.Steps which are options or alternatives are indicated with dashed linesin FIG. 5.

As has emerged from the description above, the method 500 is intendedfor use in a user terminal in a cellular communications system, and, asindicated in step 505, according to the inventive method, the userterminal applies a first timing advance value T_(TA1) to itstransmissions to a controlling node.

Also, according to the method 500, the user terminal requests, step 510,communication with the controlling node in a contention based procedureby transmitting an access request, such as MSG1 which was shown in FIG.3, in and as shown in step 515, in response the controlling nodetransmits an initiation message, such as MSG 2 from FIG. 3, for therequested communication, along with a second timing advance valueT_(TA2).

Step 520 shows the message MSG 3 from FIG. 3, i.e. a scheduledtransmission from the UE, based on the instructions in MSG 2. As shownin step 521, in one embodiment of the invention, the user terminal usesthe second timing advance value in a message which is subsequent to saidinitiation message, such as MSG 3.

Steps 523 and 524 indicate that the user terminal uses the first timingadvance value T_(TA1) if the user terminal loses the contention basedprocedure, i.e. if the controlling node subsequently continues theinitiated communication with another user terminal. The outcome of thecontention based procedure is indicated by means of MSG 4, as was alsoexplained in connection with FIG. 3.

Step 531 shows that in an alternative embodiment, the user terminal usesthe first timing advance value if the user terminal wins the contentionbased procedure.

Step 532 shows that in one version of this embodiment, the user terminaluses the second timing advance value if the user terminal wins thecontention based procedure.

In one embodiment of the invention, as indicated in step 535, the methodof the invention is applied in the case that the first timing advancevalue is considered valid by the user terminal.

Step 540 indicates that in a further embodiment of the invention, atiming advance value in a user terminal is associated with a timer andis considered valid for the duration of the timer. The timer is startedupon reception of a predefined message from the controlling node 140, sothat each of the first and second timing advance values are associatedwith respective first and second timers which have been started uponreception of respective messages.

In the embodiment where a timer is used, the user terminal can, as shownin step 545, let the timer associated with the first timing advancevalue continue running after receipt of the initiation messageassociated with the second timer, and then use the timer valueassociated with the timing advance value (T_(TAN)) which is subsequentlyused.

In another version of the “timer embodiment”, as indicated in step 550,the user terminal, upon reception of the second timing advance value,saves the value of the timer which is associated with the first timingadvance value. If the controlling node subsequently continues theinitiated communication with the other user terminal, the user terminalthen uses a timer value which is the sum of the saved value and thecurrent value of the timer of the second advance value.

In a third version of the “timer” embodiment, shown in step 555, a userterminal which has a valid timing alignment value uses this valueregardless of receipt of a second timing alignment value.

As has also emerged from the description above, although the inventioncan be used in any cellular system in which the same problem arises, ina preferred embodiment, the method of the invention is applied in an LTEsystem, Long Term Evolution, so that the user terminal will be an LTE UEand the controlling node will be an LTE eNodeB. If the method is appliedin an LTE system, the procedure in which it is employed is preferably anLTE Random Access procedure.

FIG. 6 shows a schematic block diagram of a transceiver 600 for use as auser terminal, a UE which functions according to the invention. Asindicated in FIG. 6, the transceiver 600 will comprise an antenna, shownas block 610, and will also comprise a receive part 620 and a transmitpart 630. In addition, the transceiver 600 also comprises a controlmeans 640 such as a microprocessor, as well as a memory 650.

The control means 640 and the memory 650 are used by the transceiver inorder to apply a first timing advance value to its transmissions to acontrolling node, and the transceiver further comprising means such asthe memory 650, the transmit part 630 and the antenna 610 for requestingcommunication with the controlling node in a contention based procedureby transmitting an access request such as MSG 1.

The transceiver 600 also uses the antenna 610 and the receiver 620 forreceiving an initiation message such as MSG 2 in response from thecontrolling node along with a second timing advance value. In addition,the transceiver 600 uses the control means 640 and the memory 650 forusing the first timing advance value if the user terminal loses thecontention based procedure, i.e. if the controlling node subsequentlycontinues the initiated communication with another user terminal.

In one embodiment, the transceiver will use the following components forusing the second timing advance value in a message such as MSG 3 whichis subsequent to said initiation message: the control means 640, thememory 650, the receiver 630 and the antenna 610. In this embodiment, itis also possible for the transceiver 600 to uses the second timingadvance message if the contention based procedure is won.

In another embodiment, if the contention based procedure is won, thetransceiver 600 uses the following components for applying the firsttiming advance message if the contention based procedure is won: thecontrol means 640, the memory 650, the receiver 630 and the antenna 610.

In a further embodiment, the transceiver 600 uses the control means 640,the memory 650, the receiver 630 and the antenna 610 for checking if thefirst timing advance value is considered valid by the user terminal, andin that case, for applying the first timing advance value.

Alternatively, the transceiver 600 may use the control means 640together with the memory 650 for associating a timing advance value witha timer as well as for considering the timing advance value valid forthe duration of said timer, in conjunction with which the antenna 610and the receive part 620 may be used for starting the timer uponreception of a predefined message from the controlling node, so thateach of the first and second timing advance values are associated withrespective first and second timers which have been started uponreception of respective messages.

If a timer is used, the control part 640 and the memory 650 may be usedfor letting the timer which is associated with the first timing advancevalue continue running after receipt of the message which starts thesecond timer, as well as for using the timer value that is associatedwith the timing advance value which is subsequently used.

Alternatively, if a timer is used, the control part 640 and the memory650 can be used by the transceiver 600 for saving the value of the timerassociated with the first timing advance value upon reception of thesecond timing advance value, as well as for using a timer value which isthe sum of the saved value and the current value of the timer of thesecond advance value, if the controlling node subsequently continues theinitiated communication with said other user terminal.

In a further embodiment, the transceiver 600, if it has a valid timingalignment value will use this value regardless of receipt of a secondtiming alignment value.

Suitably, as has emerged from the text above, the transceiver 600 issuitably a user terminal, a UE, in an LTE system, Long Term Evolution,i.e. it is an LTE UE.

The invention is not limited to the examples of embodiments describedabove and shown in the drawings, but may be freely varied within thescope of the appended claims.

What is claimed is:
 1. A method for uplink time alignment in a cellularcommunications system, comprising: transmitting a random access preambleto the controlling node as part of a contention based random accessprocedure; receiving a random access response from the controlling nodein response to the random access preamble, wherein the random accesspreamble comprises a second timing advance value; after receiving therandom access response, determining whether a first timing advance valuereceived from the controlling node before transmission of the randomaccess preamble is valid; if the first timing advance value is valid,transmitting to the controlling node in accordance with the first timingadvance value after receiving the random access response; and if thefirst timing advance is not valid, transmitting to the controlling nodein accordance with the second timing advance value.
 2. The method ofclaim 1, further comprising: receiving the first timing advance valuefrom the controlling node; and before transmitting the random accesspreamble, transmitting to the controlling node in accordance with thefirst timing advance value.
 3. The method of claim 1, according to whichthe user terminal uses the first timing advance value if the userterminal wins the contention based random access procedure.
 4. Themethod of claim 1, wherein: the first timing advance value is associatedwith a timer; and determining whether the first timing advance value isvalid comprises determining whether the timer is running.
 5. The methodof claim 4, further comprising starting the timer after receiving thefirst timing advance value from the controlling node.
 6. The method ofclaim 1, wherein the user terminal comprises a Long-Term Evolution (LTE)UE and the controlling node comprises an LTE eNodeB.
 7. The method ofclaim 6, wherein the method is used in an LTE Random Access procedure.8. The method of claim 1, wherein transmitting the random accesspreamble to the controlling node as part of the contention based randomaccess procedure comprises: determining that the user terminal is notallocated resources for contacting the controlling node; and in responseto determining that the user terminal is not allocated resources,transmitting the random access preamble on a physical random accesschannel to the controlling node.
 9. The method of claim 1, whereintransmitting the random access preamble to the controlling node as partof the contention based random access procedure comprises: randomlyselecting one of a plurality of preambles available for contention basedrandom access; and transmitting the randomly-selected random accesspreamble to the controlling node.
 10. The method of claim 1, whereintransmitting data to the controlling node in accordance with the firsttiming advance value comprises starting transmission of the data at atime that is offset according to the first timing advance value relativeto a nominal transmission time associated with the controlling node. 11.A user terminal for transmitting data in a cellular communicationssystem, the user terminal comprising: a transmitter arranged fortransmitting to a controlling node in accordance with a timing advancevalue; and for transmitting a random access preamble to the controllingnode as part of a contention based random access procedure; a receiverarranged for receiving a random access response from the controllingnode in response to the random access preamble, wherein the randomaccess preamble comprises a second timing advance value; and one or morecircuits arranged to: determine whether a previously received firsttiming advance value is valid when the second timing advance value isreceived; if the first timing advance value is valid, control thetransmitter to continue to transmit to the controlling node inaccordance with the first timing advance value after receiving therandom access response; and if the first timing advance is not valid,control the transmitter to transmit to the controlling node inaccordance with the second timing advance value.
 12. A user terminal foruse in a cellular communications system, the user terminal comprising: atransmitter configured to request communication with a controlling nodein a contention based random access procedure by transmitting a randomaccess preamble to the controlling node; and a receiver configured toreceive, in response to the random access preamble, a random accessresponse with a second timing advance value; one or more controlcircuits configured to: determine whether a first timing advance value,received before the random access response, is valid at receipt of thesecond timing advance value; and ignore the second timing advance valueif the first timing advance value is determined to be valid and therebycontrol the transmitter to apply the first timing advance value totransmissions to the controlling node, and otherwise control thetransmitter to apply the second timing advance value to transmissions tothe controlling node.
 13. The user terminal of claim 12, wherein the oneor more control circuits are configured to control the transmitter toapply the first timing advance value if the contention based procedureis won by the user terminal.
 14. The user terminal of claim 12, furthercomprising: a timer that is associated with the first timing advancevalue; wherein said one or more circuits is configured to the determinethe validity of the first timing advance value in relation to whetherthe timer is running.
 15. The user terminal of claim 14, wherein saidone or more control circuits are configured to start the timer whenreceiving the first timing advance value from the controlling node. 16.The user terminal of claim 12, wherein said transmitter is configured totransmit said random access preamble to the controlling node on aphysical random access channel.
 17. The user terminal of claim 12,wherein the one or more control circuits are configured to control thetransmitter to apply the first timing advance value to transmissions tothe controlling node by controlling the transmitter to starttransmission of the data at a time that is offset according to the firsttiming advance value relative to a nominal transmission time associatedwith the controlling node.
 18. The user terminal of claim 12, whereinthe user terminal comprises a Long-Term Evolution (LTE) UE.
 19. The userterminal of claim 12, wherein the one or more control circuits areconfigured to use the first timing advance value, if the first timingadvance value is valid, regardless of receipt of a second timing advancevalue.
 20. A method in a user terminal configured for use in a wirelesscommunication network, said method comprising: receiving a first timingadvance value at the user terminal; performing a contention-based randomaccess procedure, in which the user terminal attempts to access thenetwork and receives a second timing advance value; determining whetherthe first timing advance value is valid at receipt of the second timingadvance value; and ignoring the second timing advance value andcontinuing to use the first timing advance value at the user terminalfor transmitting to the network on the uplink if the first timingadvance value is determined to be valid, and otherwise using the secondtiming advance value at the user terminal for transmitting to thenetwork on the uplink.